Up two after 25 minutes, Barcelona looked en route to a typical Blaugrana Saturday. Messi was on the board as was Pedro, the young Spaniard with only his fourth goal for the season. Against a team averaging fewer than a goal-and-a-half per game, it should have been enough, particularly considering Real Sociedad was unlikely to keep Spain’s leaders off the scoresheet over the final 65 minutes. (Barcelona came into the game averaging 2.8 goals-per-65 league minutes.)

Even when Gonzalo Castro pulled one back for Sociedad minutes before half time, Sociedad could not have predicted they were on their way to a 3-2 victory over the previous undefeated Barcelona. It was only after 11 minutes of the second half that La Real could have started to dream, with a sending off leaving the hosts to play the final third of the match up a man. Castro added a second seven minutes later, and in stoppage time, Imanol Agirretxe finally put a “1” in Barcelona’s loss column.

Barcelona’s only other loss this season had been to Celtic in Champions League group play.

After the match, Tito Vilanova said he’d cautioned Gerard Piqué and halftime. Something about the match must have convinced the Barcelona head coach to reiterate the obvious. Carrying a caution into the final 45, Piqué couldn’t afford any mistakes. Yet only 11 minutes into the second period, the Barcelona defender was gone after taking down Carlos Vela.

It was the break Sociedad needed. So were the posts Messi and Pedro hit. So was the incredible performance from Castro. So was a defensive performance that limited Barcelona to three shots on goal. Not all of these breaks were luck, but for Sociedad to pull of this upset, they needed a number of things to go their way, not the least of which was their own resilient performance.

Such is the nature of unexpected results. They usually require a number of coincidental events to line up. On Saturday in San Sebastian, that’s exactly what happened.

Real Sociedad’s three unexpected points vaulted them to fifth (temporarily) while Barcelona must remain content with an 11-point lead on second place Atlético Madrid.